A Specification Driven Slicing Process for Identifying Reusable Functions

We present a new program slicing process for identifying and extracting code fragments implementing functional abstractions. The process is driven by the specification of the function to be isolated, given in terms of a precondition and a postcondition. Symbolic execution techniques are used to abstract the preconditions for the execution of program statements and predicates. The recovered conditions are then compared with the precondition and the postcondition of the functional abstraction. The statements whose preconditions are equivalent to the pre and postconditions of the specification are candidate to be the entry and exit points of the slice implementing the abstraction. Once the slicing criterion has been identified the slice is isolated using algorithms based on dependence graphs. The process has been specialized for programs written in the C language. Both symbolic execution and program slicing are performed by exploiting the Combined C Graph (CCG), a fine-grained dependence based program representation that can be used for most software maintenance tasks. The work described in this paper is part of RE2, a research project aiming to explore reverse engineering and re-engineering techniques for reusing software components from existing systems